This invention relates to a jet propulsion and prime mover unit and particularly to an improved propulsion unit for watercraft.
A particularly popular propulsion device for watercraft is the so-called "water jet propulsion unit." These types of devices include an outer housing that defines a water inlet duct through which water is drawn from the body of water in which the watercraft operates by means of an impeller mounted in an impeller housing to the rear of the water inlet duct. The water pumped by the impeller is then discharged through a rearwardly facing discharge nozzle for generating a propulsion force for the watercraft. Normally, this type of device is propelled by a prime mover that is positioned in the hull forwardly of the jet propulsion unit and which drives an impeller shaft that extends through the water inlet duct for driving the impeller.
FIG. 1 is a view that shows a conventional type of drive of this type and illustrates several of the disadvantages of it. In FIG. 1, the watercraft hull is shown partially and is comprised of an under or lower hull portion 21, above which a jet propulsion unit, indicated generally by the reference numeral 23, is supported. Forwardly in the hull from the jet propulsion unit 22, a prime mover such as an internal combustion engine 23 is supported.
The jet propulsion unit 22 includes an outer housing assembly, indicated generally by the reference numeral 24, which includes a housing portion 25 that defines a downwardly facing opening 26 that registers with a corresponding opening 27 in the hull portion 21. A duct 28 extends from this inlet opening to a portion of the housing assembly 24 in which an impeller 29 is supported for rotation. The impeller 29 is generally supported at its aft end by a combined nacelle and straightening vane portion 31. Water pumped past this portion is then discharged through a discharge nozzle 32, which faces rearwardly for generating a propulsion force to the watercraft. Frequently a steering nozzle (not shown) is supported on the discharge nozzle 32 and is pivotal about a vertically extending axis for steering of the watercraft.
In order to drive the impeller 29 from the forwardly positioned engine 23, there is provided an impeller shaft 33, which is coupled suitably to the engine output shaft 34 and which drives the impeller 29. Frequently the outer housing, and particularly the water inlet portion 25, is provided with a forwardly projecting pilot portion 35 that contains seals 36 and bearings 37 for journaling the forward end of the impeller shaft.
With this prior art type of construction, a number of problems arise. First, since the impeller shaft 33 extends through the water inlet duct 28, foreign material, indicated at 38, can easily collect on the impeller shaft 33. This foreign material can be seaweed, foreign objects, and the like. This accumulation of material not only impairs the efficiency of the jet propulsion unit but can, in extreme cases, clog it.
In addition to this defect, the forward positioning of the prime mover 23 and the use of the long engine output shaft 34 and impeller shaft 33 requires either universal joints or some type of coupling so as to accommodate axial and angular misalignments and also require very accurate positioning of the jet propulsion unit 22 and prime mover 23.
It is therefore a principal object of this invention to provide an improved jet propulsion and prime mover unit for powering a watercraft.
It is a further object of this invention to provide a jet propulsion and prime mover unit wherein the impeller of the jet propulsion unit can be driven without the necessity of shafts extending externally of the jet propulsion unit.
It is a further object of this invention to provide an improved jet propulsion and prime mover unit wherein the impeller of the jet propulsion unit can be driven by a prime mover without any drive shaft extending through the water inlet of the jet propulsion unit.
In addition to the defects aforenoted, the fact that the impeller shaft extends through the water inlet duct and since foreign materials can become entangled on the shaft, the effective cross-sectional flow area of the water inlet duct is reduced. Although this can be compensated for by increasing the size of the outer housing, this adds considerable difficulties to the desired positioning of the jet propulsion unit and adds to its bulk, which is undesirable.
It is therefore a still further object of this invention to provide an improved jet propulsion and prime mover unit for a watercraft wherein the impeller drive shaft does not extend through the water inlet duct.